(1) Field of the Invention
The present invention relates to an arrangement for an uninterruptible power supply with a rectifier, an energy store for storing electrical energy, an inverter, a switching means, and a controller. A rectifier input of the rectifier can be connected to a supply grid. The energy store is connected to a rectifier output of the rectifier and to an inverter input of the inverter. A network to be protected or a load to be protected can be connected to an inverter output. The rectifier input or the supply grid can be connected via the switching means to the inverter output, and the rectifier, the inverter and the switching means can be controlled by the controller.
(2) Description of Related Art
Various arrangements for an uninterruptible power supply, abbreviated as UPS, are known in the art. A differentiation is made between the type of an offline UPS and the type of an online UPS.
When the supply grid is undisturbed, a UPS in offline operation, also referred to as voltage and frequency dependent UPS (VFD-UPS) or passive UPS, conducts the current directly from the supply grid via the closed switching means to the network to be protected or the load to be protected. The rectifier charging the electrical energy store is also supplied from the input. When the supply from the grid is interrupted, the switching means switch over to connect the output of the inverter, which is supplied from the rectifier or the energy store, with the network to be protected or the load to be protected.
When a UPS operates online, also referred to as voltage and frequency independent UPS (VFI-UPS), continuously operating UPS, dual converter UPS and the like, the supply grid is connected to the input of the rectifier charging the energy store. The network to be protected or the load to be protected are supplied from the inverter, wherein the inverter receives the required energy from the rectifier when the supply grid is undisturbed, meaning that the grid voltage is present at the rectifier input, and is supplied from the energy store in the event of a grid failure.
The AC voltage at the inverter output is generated by the inverter from the DC voltage of the so-called DC link circuit between the rectifier and the inverter.
For enhancing the security of supply with a VFI-UPS, the switching means which connects the supply grid via by the rectifier and the inverter with the network to be protected and/or the load to be protected, when the rectifier and the inverter operate undisturbed, enables a so-called bypass circuit, which connects the supply grid and the network to be protected or the load to be protected via the switching means by bypassing the rectifier and the inverter. When a fault occurs in the rectifier or inverter, the connected load is switched over to this bypass and supplied with power without interruption.
The topology of an offline UPS and an online UPS may be identical. They can mainly be distinguished by the different position and task of the switching means. With a suitable layout of the components of a UPS and a suitable control, an offline UPS can hence be converted into an online UPS and vice a versa.
In an online UPS manufactured and distributed by the applicant, the controller includes three control parts which are connected via a CAN-BUS, wherein one control part is provided for controlling the rectifier, one control part for controlling the inverter, and one control part for controlling the switching means. Each control part has an integrated dedicated auxiliary current supply for supplying the control part with auxiliary current. If a control part or an auxiliary current supply powering the control part fails, then this control part is unable to contribute supplying the grids or loads connected to the UPS.
Moreover, sensors for measuring different electrical parameters at the input and/or the output of the rectifier or of the inverter or at other locations of the UPS are integrated in each control part. To this end, each control part is connected to the measurement locations via measuring lines. Sometimes, high voltages may be present at the measuring lines which may be exposed to disturbance sources, which may cause faulty measurement results unless adequate measures are taken to prevent a disturbance of the measurement.
It is therefore the object of the invention to improve an arrangement for an uninterruptible power supply of the aforedescribed type so as to increase the reliability and reduce the susceptibility to disturbances. In particular, the susceptibility of the measurement of electrical parameters to disturbances should also be reduced.